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Date May 2018 Marks available 1 Reference code 18M.2.SL.TZ1.S_1
Level Standard Level Paper Paper 2 Time zone Time zone 1
Command term Find Question number S_1 Adapted from N/A

Question

Let f(x) = ln x − 5x , for x > 0 .

Find f '(x).

[2]
a.

Find f "(x).

[1]
b.

Solve f '(x) = f "(x).

[2]
c.

Markscheme

* This question is from an exam for a previous syllabus, and may contain minor differences in marking or structure.

f ( x ) = 1 x 5      A1A1 N2

[2 marks]

a.

f "(x) = −x−2      A1 N1

[1 mark]

b.

METHOD 1 (using GDC)

valid approach      (M1)

eg 

0.558257

x = 0.558       A1 N2

Note: Do not award A1 if additional answers given.

 

METHOD 2 (analytical)

attempt to solve their equation f '(x) = f "(x)  (do not accept 1 x 5 = 1 x 2 )      (M1)

eg   5 x 2 x 1 = 0 , 1 ± 21 10 , 1 x = 1 ± 21 2 , 0.358

0.558257

x = 0.558       A1 N2

Note: Do not award A1 if additional answers given.

[2 marks]

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Topic 5—Calculus » SL 5.3—Differentiating polynomials, n E Z
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